What is Current transformer: Definition and 24 Discussions

A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
Current transformers, along with voltage or potential transformers, are instrument transformers. Instrument transformers scale the large values of voltage or current to small, standardized values that are easy to handle for measuring instruments and protective relays. The instrument transformers isolate measurement or protection circuits from the high voltage of the primary system. A current transformer provides a secondary current that is accurately proportional to the current flowing in its primary. The current transformer presents a negligible load to the primary circuit.Current transformers are the current-sensing units of the power system and are used at generating stations, electrical substations, and in industrial and commercial electric power distribution.

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  1. K

    Voltage measurement on a Current Transformer (CT)

    I don’t know the ratio of the CT. I’m just looking for an explanation on this. I thought in order to measure output voltage you need to pass the current through a resistor and read the voltage drop. A co worker put 400a through the CT and measured 130v. Something just seems off to me. Can you...
  2. B

    Current Transformer Proton Accelerator

    Suppose you place a current transformer into a vacuum and flow ionized hydrogen through the center of it. The ionized hydrogen would act as the secondary winding of the current transformer. How specifically would the acceleration that the hydrogen ions experience be calculated?
  3. B

    Can energy be extracted from a proton beam using a current transformer?

    Suppose there exists a proton beam that is pulsed on and off. If this beam is aimed through a current transformer as in the attached image (the proton beam would act as the main primary conductor in this case), what would be the output of the transformer, and how would it affect the beam...
  4. Manoj Sahu

    Why do Current Transformer cores have different knee point voltages?

    I have to test a Current transformer. I read knee point is a point at which 10% increase in voltage leads to 50% increase in current. As there are different classes of current transformer (cores), how it is decided what/how much will be the knee point voltage of that core.
  5. S

    The use of current transformers

    Hello everyone, Recently, i have designed a capacitor bank for a company which they already have their main switch board with metering stuff. The ammeter of the main switch board has its own CTs but for the capacitor bank I need to install a CT separately. The spec of existing CTs for main...
  6. G

    I Induced EMF in a half vs. whole ferrite toroid

    Hello all - I've stumbled upon what seems to be a pretty basic magnetic materials question that's got me stumped. Maybe one of you can help me figure this out. I did the following experiment (see figure below): Put a ferrite toroid around a current carrying wire carrying 12 Amps RMS at 120V...
  7. G

    Can a time-varying magnetic field pass a metal sheet?

    Hello. I'm using CT (Current Transformer) to measure the current flowing on the power line. The frequency of the current is 13.56 MHz. CT appeared to be metal-shielded (This metal case of CT may be grounded when CT is used). CT has a toroidal shape and the power line under the measurement...
  8. Nikhil N

    Current transformer for coupling noise into a cable

    I want to couple white noise to a communication cable. I am using a 50/5A CT. My idea is to connect the noise in the secondary and to couple that noise into the cable. I want to know will my idea work? Does the CT what I am using will be suitable?
  9. R

    Utility Metering Current Transformer

    The electric utility has a digital wattmeter that seems to be measuring the power usage at the high voltage side of our distribution transformer (11 kV - 420 V 3 phase, 250 kVA) via a Current Transformer. How exactly does this work? Specifically, what I'm confused about is that transformers...
  10. cnh1995

    Switching transient in current transformer

    If a purely inductive circuit is excited with an AC source, a transient occurs before reaching the steady state 90 ophase shift i.e. the current takes some time to shift the phase depending on the switching instant. Is there any such transient in CT?? Suppose the primary circuit is initially off...
  11. cnh1995

    Current Transformer Magnetic Behavior

    Hi friends..I am very confused with the magnetic behavior of a CT. CT secondary should never be left open.Okay I understand why. But how exactly does a shorted secondary cancel the primary flux? For that the primary and secondary currents must be 180 degrees out of phase while Lenz's law states...
  12. B

    Current transformer for protection question

    Homework Statement Determine RR value if the relay current has not to exceed 20mA. Neglect relay resistance. 2. The attempt at a solution I believe the solution is behind Merz-Price theorem, where the voltage system is balanced. CT1 and CT2 are identical current transformers, however, RL2...
  13. D

    Zero Impedance in Oscillating current transformer

    Hi, I have read Steinmetz books and he has a very good example of OC phenomenon that is nothing like AC case. There are certain conditions under which an OC transformer has zero impedance. Also, on his chapter of long transmission lines, he says quarter wave resonance using abrupt pulses can...
  14. R

    Information about current transformer

    hello friends...i am facing difficulties in understanding the difference between live type and deadtpe current transformer...and also the advantage of live type over dead type?
  15. S

    Using wattmeter with current transformer

    Hey guys, Just looking for some reassurance as to whether I have visually depicted the wattmeter and current transformer correctly in the image I have provided. Needed to step down current to satisfy current ratings of wattmeter. One thing I cannot seem to see is how it detects the voltage...
  16. C

    Current Transformer Phasor Diagram Explained

    can anybody explain me the phasor diagram of a current transformer. it would be a great help
  17. A

    Current transformer polarity and power flow

    Hello i need to know , does the polarity of the current transformer affects the power measurements in AC systems, and if it does , how it affects the power measurements knowing that in measuring power we use the RMS values anybody have any idea about this ?? that's to say , if you have...
  18. A

    Phase angle error in current transformer

    Homework Statement hi in current transformer the primary current lags the secondary current by an angle..to determine the %ratio error we need to measure the ratio of primary and secondary current...so we use a RC circuit to lead the primary current so that it could be in same phase as...
  19. B

    Questions related to Current Transformer and Gauge Factor?

    Hello Friends, Kindly tell me the formula/values for the following: 1. Gauge Factor in the primary winding of a transformer with voltage 5 MVA 2. Voltage Drop in the Secondary Side of a Current Transformer with 100:5 Please help Thanks
  20. A

    Current transformer output

    i can't seem to understand why with current transformer if the primary winding is reconnectable the rated output stays the same. but rated output depends on turn ratio if the secondary winding is reconnectable?? why??
  21. J

    Is Oversizing Current Transformers Necessary for Timed Overcurrent Protection?

    I am using a digital genset controller that to run and protect a generator. This controller has, in addition to other functions, timed overcurrent protection (1-30 seconds). The controller uses 5 amp secondaries. The generator is 83 amp. The 100 amp breaker I plan to use has a...
  22. B

    Why does the magnetic flux in a CT core decrease with connected load?

    Hi Guys, :smile: I am grappling with a peculier (but somewhat common) problem with Current Transformer (CT) magnetic circuit. I will be very grateful if someone could help me out with my problem. 1)In an ideal Voltage Transformer (VT), the magnetic flux developed in the core remains...
  23. Z

    Power Generated by a Toroidal Current Transformer

    I'm building various current transformers for a project at work and having trouble finding out what the best core material is to generate the most power from a 7kV power line using inductance. I have seen that Silicon-Steel provides the greatest flux density saturation but have heard that some...
  24. M

    Core balance current transformer

    Hi Can anybody help me in getting technical information about core balance current transformers. Thanks Mahadev